The transport of ADP, the substrate of oxidative phosphorylation, into the matrix of mitochondria is a carrier-mediated process in which an ADP molecule is conveyed into the matrix in exchange for an ATP molecule, which is then transported out of the mitochondria. Under physiological conditions, the rates of both substrate oxidation and oxidative phosphorylation in normal tissue mitochondria are limited by the availability of ADP and the ATP/ADP ratio, indicating that the mechanism of the nucleotide translocation is specific and under strict control. Many malignant cells differ significantly from normal cells in the integration of glycolysis and respiration. This project will study whether in these tumor cells the adenine nucleotide transport in mitochondria is altered either kinetically or with respect to its specificity. Together with an unmasked adenosine triphosphatase activity, the excessive regeneration of ADP and Pi in the cytoplasm may be the cause for the high rate of lactic acid formation observed in many tumor tissues. This project is first aimed at quantitatively determining the rates and the specificity of adenine nucleotide translocation and the level of the ATPase activities in isolated mitochondria from several tumor tissues of various degrees of dedifferentiation and at seeking possible correlations between these activities and the degree of tumor malignancy and the rate of tumor growth. During the past year, we obtained results that indicate a possible futile cycle of ADP transport across the tumor mitochondrial membrane and, therefore, renders inefficient oxidative phosphorylation in tumor tissues. In addition, the cholesterol levels in the inner mitochondrial membrane of these hepatomas were elevated several times higher than that of normal liver tissue with a resultant nucleotide transport characteristically different from that of normal liver tissue (manuscript in preparation). (E)